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To Alpha Centauri via Hawai’i

I’m always looking for ways to relate interstellar distances to common objects on Earth, knowing that misunderstandings about the vast scale of the universe are common. Sir John Herschel (1792-1871) talked about dropping a pea off the side of a ship after every mile on an ocean voyage the distance of the nearest star, telling his readers that it would require ‘a fleet of 10,000 ships of 600 tons burthen, each starting with a full cargo of peas.’ Herschel was the first to try to measure the distance to Alpha Centauri, and while his numbers weren’t as accurate as ours, he captured for his era the disconnect between Earthly distances and the heavens. Larry Klaes weighs in this morning with yet another way to study the issue, using an exhibition on the interplanetary scale that has now been extended Herschel-style to the ultimate voyage.

By Larry Klaes

Since its dedication in 1997, the Sagan Planet Walk has become a landmark feature of downtown Ithaca, New York. The various monuments, or “stations”, representing the major places in the Solar System from the Sun to Pluto serve first as a memorial to the late Cornell astronomer and science popularizer Carl Sagan. Perhaps best known for his Cosmos television series which premiered on PBS in 1980, Sagan passed away in December of 1996 at the age of 62 after two decades of teaching at the university.

The Sagan Planet Walk also serves as a continuing educational tool about our celestial neighborhood. Among its astronomy informational features is the Walk’s physical demonstration of just how far apart objects in our Solar System really are on a scale that the general public can relate to. When reduced from its actual radius of five billion miles, the Solar System’s scale becomes clear in everyday terms. The gray marble Sun station resides prominently in the Ithaca Commons with the planets from Mercury to Mars nearby, while the Pluto station sits just outside the Ithaca Sciencenter nearly one mile away. The Sciencenter is the primary developer of the Sagan Planet Walk.

One question that has often been asked by folks who hiked the Sagan Planet Walk is just how far away the stars nearest to our Sun would be on this scale. The answer is that a station for this feature of the Walk would have to be located in tropical Hawai’i over five thousands miles west of temperate Ithaca. That is how far one would have to travel to reach the representation of our nearest suns, the Alpha Centauri system, which exists 4.3 light years away, or over 25 trillion miles across interstellar space.

Image: The beginning of the Sagan Planet Walk, a gray marble monument symbolizing the Sun. Bring your walking shoes if you’re headed for the Pluto station. Alpha Centauri will require plane tickets. Credit: Andrew Alden.

For the last two years, the Sciencenter has been partnering with Cornell, the University of Hawai’i, and NASA to place an Alpha Centauri station on the Big Island of Hawai‛i at the ‘Imiloa Astronomy Center on the Hilo campus of the University of Hawai‛i. Lead funding was provided by the NASA Space Grant Program of New York (based at Cornell) and Hawai‛i (based at the University of Hawai‛i), with additional major funding provided by ‛Imiloa and the Sciencenter.

A dedication ceremony to mark this newest and most distant addition to the Sagan Planet Walk will be held on September 28 at the ‘Imiloa Astronomy Center to coincide with the annual Polynesian Voyaging Festival at the hands-on science center, which focuses on astronomy and the culture of Polynesian voyaging. The features of the festival are to include presentations of double-hulled, ocean-going canoes, live demonstrations, and other activities that celebrate the proud heritage associated with centuries of Pacific Ocean crossings without instruments. Among those present at the dedication will be Charlie Trautmann, executive director of the Sciencenter and adjunct professor of engineering at Cornell.

While retaining the basic features common to all the stations of the Sagan Planet Walk – placards with interesting facts and a proportional model of each world that invites visitors “to contemplate the enormous, awe-inspiring scale of the Universe and our place within it” – the Alpha Centauri station also reflects the culture of its surroundings (Kamailehope is the Hawaiian name for Alpha Centauri).

The centerpiece of the exhibition is a large stone Hawaiian figure, sculpted in native Hawaiian volcanic stone by world-renowned Hawaiian artist Rocky Jensen. On either side of this sculpture are four graphic panels which detail the scale of the Solar System in both English and Hawaiian, the connection with the Sagan Planet Walk in Ithaca, and how the Alpha Centauri stars were utilized by Polynesian sailors to cross the Pacific in their open, double-hulled canoes without the need for astronomical tools. Native Hawaiian school children will learn about their heritage and the history of navigation thanks to an eight-foot wide circular star compass which completes the station.

Image: The Alpha Centauri station of the Sagan Planet Walk, fittingly found under Polynesian skies. Credit: Ithaca Sciencenter.

“The inclusion of the Alpha Centauri station has been fifteen years in the making, so we’re excited to see it coming to fruition and completing the Sagan Planet Walk,” said Teresa Smith, Public and Media Relations Manager at the Sciencenter.

The day after the Hawai’i dedication ceremony, the Sciencenter will hold its own celebration of the Sagan Planet Walk expansion to our nearest stellar neighbors by offering a free tour of the Walk, guided by Greg Sloan of Cornell’s Astronomy Department. Tour members will meet up at the Sun station on the Commons and make their way through the Solar System to the Pluto station at the Sciencenter, where prepared Hawaiian refreshments will await.

The newly expanded Sagan Planet Walk is now the largest such exhibition on Earth, measuring five thousand miles from end to end. This eclipses the previous record of 66 miles held by the artwork in the Stockholm, Sweden subway tunnels.


Comments on this entry are closed.

  • d.m.falk September 24, 2012, 10:56

    It even looks like a Moai! ;)

    To be fair, there needs to be a second Alpha Centauri station for Alpha Centauri B, and perhaps a third for Proxima Centauri, somewhere…but where I don’t know…


  • Gregory Benford September 24, 2012, 12:27

    Jon Lomberg, who worked with Sagan on COSMOS as art director, lives on the big island…did he have a hand in this?

  • Paul Gilster September 24, 2012, 12:30

    Greg, it’s hard to imagine he didn’t, given his work on the Galaxy Garden and his connection with both Hawaii and Sagan. But I’ll have to find out for sure.

  • Didac September 24, 2012, 12:54

    d.m.f is right about Alpha Centauri. In this scale, Alpha Centauri A and Alpha Centauri B can be a mile far away from each other. The problem is that Proxima Centauri lies in the Ocean, hundreds of miles from Hawai’i.

  • John G September 24, 2012, 13:33

    For the next step up in galactic distances:
    the nearest galaxy of substantial size (Andromeda, aka M31), would be 30 billion miles away to the same scale

  • andy September 24, 2012, 13:46

    Hopefully in the not too distant future we will be able to extend the walk by putting some planets at the Alpha Centauri end…

  • Mike September 24, 2012, 14:34

    To Andy, I’m expecting we’ll get some news about that before the end of the year. But you do realize at the scale of the planet walk it maybe a very short extension for Alpha Centauri planets? But that doesn’t lessen the thrill of finding planets at our next-door neighbour.

  • ljk September 24, 2012, 14:58

    John G September 24, 2012 at 13:33:

    “For the next step up in galactic distances:
    the nearest galaxy of substantial size (Andromeda, aka M31), would be 30 billion miles away to the same scale.”

    A Sagan Planet “Walk” station on one of the Kuiper Belt Objects (KBO) might do for the Andromeda galaxy.

    Why am I suddenly thinking of the Stephen Wright joke about his owning a full-scale map of the United States, where one inch equals one inch. Then he folded it.

    Here is another interesting celestial scale analogy: If the entire Sol system out to Pluto were shrunk down to where you could hold it in the palm of your hand, the Milky Way galaxy in proportion would still be the size of the North American continent.

    Speaking of Jon Lomberg’s Galaxy Garden on Hawai’i:


    Add the Keck Observatory on Mauna Kea to the Garden and the Alpha Centauri station and any astronomer worth his or her salt would have more than the beaches as reasons to visit the islands.

  • Ron S September 24, 2012, 15:49

    I just did a quick calculation and determined that the Alpha Centauri system is moving toward us (radial motion) at a current rate of ~4.5 AU/year. Does that rock have wheels? ;-)

  • andy September 24, 2012, 16:01

    P.S. shouldn’t that be an ʻokina rather than an apostrophe in Hawaiʻi?

  • Astronist September 24, 2012, 16:28

    My own favourite model is the one which relies on the coincidence that the ratio of a mile to an inch (63360) is almost the same as the ratio of a light-year to an astronomical unit (63284). If you then draw on a piece of paper a circle with radius one inch, that models the orbit of the Earth. The Solar System out to the orbit of Neptune then fits on a large table-top, though to reach Sedna at aphelion you’d need to go to the bottom of the garden. Alpha Centauri is then 4.4 miles away, or the distance you can walk in an hour or so.

    The beauty of this model for me is that it makes clear the difference between interplanetary and interstellar space using distances which are within everyone’s everyday experience.


  • Christopher Phoenix September 24, 2012, 16:49

    This should clear up the size/distance confusion many people have about the universe. Traveling 4.3 LY, or 25 trillion miles, is going to be a much larger challenge than cruising about our own solar system.

    Even more stupendous are intergalactic distances. If our own Milky Way were reduced to the size of a penny, the Andromeda Galaxy would be 23 inches away, the Virgo Supercluster 50 feet away, and the nearest quasar 3C273 is a little over two miles away. The horizon of the visible universe, 13.7 billion LYs away, would be about 20 miles from the Milky Way penny. It would be pretty cool to make a scale model of the visible universe, with each galaxy represented as a scale, glowing model in glass.

    If we had FTL drives that traveled 36,500,000 times faster than light (fast enough to cross the Milky Way the long way in a single day), we could reach the Andromeda Galaxy in under a month- our sphere of travel and exploration will not be merely galactic, but intergalactic in scope!! Our 36.5 million times faster-than-light intergalactic spaceships could reach any galaxy in our local group in under three months. So, if we can travel within our galaxy in mere days like in some SF stories, we should be able to travel to other galaxies as well. And yet, this vast scope of travel would be measured in inches and feet on the two-mile wide scale model of the visible universe…

    I can’t help but wonder how we would hope to keep track of such vast “island universes” if we did travel between galaxies- there are 400 billion stars in the Milky Way alone, 40 billion in the Triangulum Galaxy, and 1 trillion stars in Andromeda- even if only a fraction of these stars have potentially habitable planets, there would be countless billions upon billions of planets to explore.

  • Tony Mach September 24, 2012, 18:04

    Well, if you going to mention the largest art projects on Earth, you need to mention Ze Frank’s “Earth Sandwich”:

    Nitpickers of the world, unite!


  • andy September 24, 2012, 18:26

    But you do realize at the scale of the planet walk it maybe a very short extension for Alpha Centauri planets?

    Sure. But it is an interesting scale though. We have one of these planet walks near where I live, last time I went there I realised that by the time I’d got to Mercury, I would have gone past all four of the known planets around Gliese 581 and have left that system’s habitable zone behind me, while it would still be a long walk to Pluto…

    (Incidentally the latest part of the debate over the number of planets at Gliese 581 appeared on the arXiv last week, declaring planets f and g to be illusions and for good measure coming perilously close to dropping planet d into the red noise.)

  • Digbijoy September 24, 2012, 20:18

    Christopher Phoenix

    Continuing on your idea, I have always wondered, ‘what if we can actually travel to Andromeda galaxy and explore the billions of planets it hosts?’ … I wonder, if humanity continues to progress/advance at the present rate, then what will be a tentative timeline when we can actually make such a trip to Andromeda feasible? And if we can have such space-ships using which we can make round trips around Milky way in a day, then we can map out the details of all the stars and the planets in Milky Way in a span of a year or so, assuming a thousand dedicated people make 1-day trips around Milky Way every day !… Soon after that, we can map out details of all stars & planet in other galaxies.. we shall know for sure, with precise details, which planets host life and in which star systems and in which galaxies, and what ‘types’ of life ! Won’t that be cool ? I asked one of my colleagues what if we could do so, and he replied that, that’s arrogance ! .. with such limited knowledge & technology (in a cosmic scale), to think of making inter-galactic travels (as of now) is simply arrogance. He also added that if we can map out the details of all planets across all stars in almost all galaxies, then we become God (if God exists, that is).

    But I then feel sad that such things won’t happen for sure in my lifetime, and that I will die one day wondering and wishing – ‘Oh if only we, humans, could make a trip to other stars, other galaxies!..Oh I wish I knew if any planet hosted intelligent life in Milky Way or even in another galaxy’ … just a futile wish :-)

  • Rob Henry September 25, 2012, 19:56

    All these descriptions seem in aid of explaining what differences of N orders of magnitude should equate to – the problem being that a feel for this problem is not given as a general part of schooling . Actually when giving such rough results its also easy to make (and for others to pick up on these mistakes).

    Thus I noticed that John G’s placing Andromeda at 30 billion miles when Hawaii is is at Alpha Centauri’s distance is at least an order of magnitude too high – even though I have only a ballpark idea of how far this island is from the Sagan walk.

  • Colin Weaver September 25, 2012, 20:38

    Actually, the Solar System Drive in Australia, at 205km, is significantly larger in span than the Stockholm subway. It starts in Dubbo, NSW with Pluto, and ends 205km away at Siding Spring Observatory near Coonabarabran, NSW representing the sun.


  • ljk September 26, 2012, 12:29


    OMG SPACE is the thesis project of Margot Trudell, an OCAD graduate of the graphic design program in Toronto, Canada. This website aims to illustrate the scale and the grandeur of our solar system, as well as illustrate through the use of infographics our work in the exploration of our solar system with various spacecraft.


    Despite all the work that scientists are putting into space exploration and research, and all that we’ve learned and acheived over the past half-century, the general public isn’t very aware of it. I believe that this is mostly due to how this information is communicated to the general public, in a very academic and scientific manner. It’s hard for most people without backgrounds in these areas to really comprehend what it means when we send a probe past Jupiter or how far away Eris really is, and it’s simply difficult to truly grasp the magnitude of our solar system and all its celestial inhabitants. Thus, I decided that visuals would greatly help people’s understanding of space and our achievements in space exploration, and as a graphic designer I was more than excited to get to work.


    All the planets on this website are to scale, including the sun and dwarf planets. The distances between each object and the sun are also to scale, and both the planets and relative distances are to scale with each other. Everything is calculated at a ratio of 1:647 to make easier numbers to work with and give me reasonable pixels sizes for this website. So if the Sun is 1,391,000 kilometers in diameter, then 1,391,000 divided by 647 equals 2149.92, and if I convert kilometeres to pixels where one kilometer is one pixel, my image of the sun is 2149 pixels squared. The same works for the distances: if Mercury is 57,909,050km from the Sun, with the ratio of 1:647, the distance is boiled down to 89503.94, so 89,503 pixels from where the Sun is placed on the screen. With everything calculated using the same ratio, all the sizes and distances are then properly to scale relative to one another.


    The information used to create the contents of this website is accurate as of early 2011. Information has not been updated since then, so mission status’ and intentions may have changed since then, as well as our understanding of our solar system and our knowledge of its contents, and those changes are not reflected here (this mainly applies to current and future missions).

  • Christopher Phoenix September 26, 2012, 20:59


    Well, given that quick voyages across the galaxy and to other galaxies requires FTL star drives, most people’s answer to your question would be a flat “never”. Then again, perhaps our descendants will discover new physics that allows them to stabilize wormholes or warp space to enable ultra-fast transit between galaxies- who knows? There may yet be loopholes in undiscovered physics that allow us to dodge around the light-speed barrier, much as time dilation went unnoticed by Newton’s Laws for centuries. Even so, stabilizing wormholes or warping space is probably a job for an ambitious Type 2 civilization, so I’d guess a few centuries will have passed before widespread interstellar travel even if we do invent a breakthrough interstellar drive.

    It would be really cool if we could explore the Milky Way and the nearby galaxies, find out which planets within which star systems support life, and perhaps classify all the different types of life that appear throughout the Local Group (such classification systems appeared in old space opera stories like E.E. Doc Smith’s Lensman series!!). Just imagine seeing a vast galactic star map with all the habitable planets and home worlds of intelligent beings marked! Did you calculate that a thousand dedicated individuals could map the galaxy in a year yourself? If so, I’d love to see your calculations. I’ve always wondered how long it would take to map our galaxy.

    I don’t really understand your colleague’s statement that exploring neighboring galaxies will make us into gods, though, unless he means that we would be gods compared to us in the way that the crew of a crashed jetliner might be hailed as visiting deities by a stone age tribe. Across the galaxy and as many others as we choose to visit in our hypothetical intergalactic spaceship, we will find many things we don’t completely understand. Every planet we visit will be as complex as Earth ever was, with as varied and intricate a history. With billions of planets to visit, we can’t explore them all. Nor could human minds contain and process all the information that could be gathered from the billions of planets that may exist in the Milky Way. Knowing that several tens of billions habitable planets exist in the Triangulum Galaxy hardly classifies as omniscience. Can you imagine how much surface area a couple billion planets has to offer? Imagine combing every single one for undiscovered species of insect-sized organisms. Still feel omniscient? ;-) It is like playing with grains of sand on the beach- you can play on the beach, but you can’t know every grain of sand in every beach across the whole Earth. The universe is just too big.

    Neither would we qualify for omnipotence, even with all the fancy technological toys that galactic space travelers could possess. Technology has limits and can fail- especially in hostile unexplored environments, and its users are limited by their knowledge (or the lack thereof) and biology. Cosmic rays can kill us (or damage circuitry), vacuum destroy us, extremes of temperature freeze or boil us, and so on. Even if we modified our bodies for extreme endurance, we will still have clear limits. We make mistakes. Our technology can fail. We will encounter situations we did not expect. Just look at modern day space travel. Encountering an advanced hostile alien species or getting marooned could doom a starship’s crew, or at least threaten their survival. So, no, intergalactic space travelers won’t become all knowing and all powerful, any more than possessing satellites and nuclear missiles made us anything more than humans with some sophisticated (and dangerous) technology. We’ll just be humans with some fancy technological toys, powerful up to point but just as mortal as modern humans.

    But, are these all but futile dreams? Maybe- but so were heavier-than-air flight and space travel in the 19th centuries, or even the laser just before it was invented. Impossible dreams inspire young minds to learn more about the universe around them. As a result of my interest in space travel, I have resolved to learn more about general relativity, quantum mechanics, and astrophysics. On the whole, I think our whole society would be much better off if we focused our energies on achieving “impossible” dreams like interstellar flight rather than bickering over resources and conducting futile wars. And who knows- maybe studies into breakthrough propulsion will turn up something. :-)

  • ljk September 27, 2012, 12:41

    The Cornell Chronicle’s take on the new addition to the Sagan Planet Walk:


  • ljk September 30, 2012, 16:26


    The Center is Everywhere

    David H. Weinberg

    (Submitted on 23 Sep 2012)

    “The Center is Everywhere” is a sculpture by Josiah McElheny, currently (through October 14, 2012) on exhibit at the Institute of Contemporary Art, Boston.

    The sculpture is based on data from the Sloan Digital Sky Survey (SDSS), using hundreds of glass crystals and lamps suspended from brass rods to represent the three-dimensional structure mapped by the SDSS through one of its 2000+ spectroscopic plugplates.

    This article describes the scientific ideas behind this sculpture, emphasizing the principle of the statistical homogeneity of cosmic structure in the presence of local complexity.

    The title of the sculpture is inspired by the work of the French revolutionary Louis Auguste Blanqui, whose 1872 book “Eternity Through The Stars: An Astronomical Hypothesis” was the first to raise the spectre of the infinite replicas expected in an infinite, statistically homogeneous universe. Puzzles of infinities, probabilities, and replicas continue to haunt modern fiction and contemporary discussions of inflationary cosmology.


    7 pages, 2 figures. For related articles see arXiv:1006.1012 and arXiv:1006.1013


    Popular Physics (physics.pop-ph); Cosmology and Extragalactic Astrophysics (astro-ph.CO)

    Cite as:

    arXiv:1209.5113 [physics.pop-ph]

    (or arXiv:1209.5113v1 [physics.pop-ph] for this version)

    Submission history

    From: David H. Weinberg [view email]

    [v1] Sun, 23 Sep 2012 21:13:26 GMT (909kb)

  • johnq October 1, 2012, 21:06

    My favorite comparison measure for the distance to Alpha Centauri came from a Boeing engineer involved with the Apollo program. He had been interviewed by the Seattle Times and the interview was printed Sunday, July 20, 1969. Unfortunately, I do not remember the man’s name or what became of him.

    He said that he liked to think of the saying that a journey of a thousand miles begins with a single step. On that basis (and I think may reconstruction of his arithmetic is correct), if Alpha Centauri was assumed to be 1000 miles away, than the journey to the moon in comparison was something on the order of .6 inch (length of the big toenail?). Hardly a step but you got to start somewhere.

    You can continue the analogy and roughly — in an order of magnitude sort or way — a step or two, something like a few feet, would represent a journey to Mars. So Mars would be the true first step on our way to the stars. And that sounds right.

  • J-Sun October 3, 2012, 16:33

    Strange to describe the Planet Walk as being completed by this when it isn’t a planet and can’t be walked to from the rest of it but, while it may now be the largest, as others have pointed out, the Sweden subway tunnels would not have been the largest. My nominee (and there may be larger still) would ironically be both in Sweden and similar to the Planet Walk, 950 KM from the Sun to the termination shock:


    The Somerset Spacewalk is between the two in size. But the Sagan Space Walk has the advantage of being initially the smallest – you can’t represent Alpha Centauri on earth in the other two. :) Also odd that all three of these (though there are likely more) were begun/opened/inaugurated/dedicated in 1997-8.

    (First time I’ve posted here (even if it’s a late post) so I wanted to say this is probably the best website on the web – I’ve been reading it for months now, I guess, and I love it.)

  • ljk October 5, 2012, 12:15

    Cornell’s student newspaper, the Daily Sun, reported on this event, in particular the ceremony that took place in Ithaca the day after the Hawai’i one:


    Of somewhat sad note at the very end of the CDS article, and I quote:

    “Correction: A previous version of this story incorrectly stated the society to which Arthur Samplaski belongs. It is the Cornell Astronomical Society, not the Cornell Astrological society.”

    Apparently that word was put in the news item even after the CAS member saw what the reporter wrote and corrected her on the spot. Good thing Carl Sagan wasn’t around to see that astrological – I mean astronomical – blunder.

  • ljk February 11, 2013, 15:34

    Not only is the Universe vast in diameter but it is also incredibly vast when it comes to the number and types of objects that make it so.

    Here is an article on this subject plus a video:


    I know there will be those who will complain about this statement, but I tend to side with the idea that if you have a lot of celestial objects which are conducive to the creation and sustainment of life, like stars, then it will increase the possibility that there are other beings in the Cosmos. Whether they can all think and build starships and send signals is another matter, but this just means we really have to get out there and find them.